The following income of a local authority is exempt from tax:
a) Income which is chargeable under the head “Income from house property”, “Capital gains” or
“Income from other sources” or
b) Income from a trade or business carried on by it which accrues or arises from the supply of a commodity or service (not being water or electricity) within its own jurisdictional area or
c) Income from business of supply of water or electricity within or outside its own jurisdictional area.